This invention relates to a method for processing images to recognize materials by means of X-rays in which the X-rays, emitted by a radiation source, have different energy spectra. The X-rays which penetrate an article, such as a piece of luggage containing the materials to be examined, are received by a detector, converted into signals and evaluated by a computer system.
The X-rays transilluminate the articles, such as pieces of luggage, for classifying the materials carried therein to prevent luggage holding prohibited items, for example, explosives, from clearing the safety checkpoints.
An apparatus for transilluminating luggage with X-rays is disclosed, for example, in German Offenlegungsschrift 31 42 759. The luggage is subdivided visually into local, narrow strips which are transilluminated with X-rays emanating from two X-ray sources. The weakening of the X-rays is measured at least by one line or strip-like bank of detectors and applied to an image memory. In order to obtain an overall image of the examined luggage, the separately stored measuring values obtained from the rays of the different X-ray sources are recombined by means of an electronic image processing system into a single image after the passage of the luggage.
A method for detecting luggage containing prohibited items is disclosed, for example, in German Patent No. 44 06 956. According to the method described therein, the luggage is examined in a multi-stage detector arrangement in which in a lower process stage a subdivision of the luggage into at least a two-dimensional coordinate system is effected and in a higher process stage exclusively a local examination of those luggage zones takes place which have not been unequivocally cleared.
It has been found in practice, however, that the above-outlined methods are time-consuming because the results are available only after a complete passage of the luggage and thus only after the construction of the overall image.